This study was conducted at the Yuma Valley Agricultural Center. The soil was a silty clay loam (7-56-37 sand-silt-clay, pH 7.2, O.M. 0.7%). Spinach ‘Meerkat’ was seeded, then sprinkler-irrigated to germinate seed Jan 13, 2025 on beds with 84 in. between bed centers and containing 30 lines of seed per bed. All irrigation water was supplied by sprinkler irrigation. Treatments were replicated four times in a randomized complete block design. Replicate plots consisted of 15 ft lengths of bed separated by 3 ft lengths of nontreated bed. Treatments were applied with a CO2 backpack sprayer that delivered 50 gal/acre at 40 psi to flat-fan nozzles.
Downy mildew (caused by Peronospora farinosa f. sp. spinaciae)was first observed in plots on Mar 5 and final reading was taken on March 6 and March 7, 2025. Spray date for each treatments are listed in excel file with the results.
Disease severity was recorded by determining the percentage of infected leaves present within three 1-ft2areas within each of the four replicate plots per treatment. The number of spinach leaves in a 1-ft2area of bed was approximately 144. The percentage were then changed to 1-10scale, with 1 being 10% infection and 10 being 100% infection.
The data (found in the accompanying Excel file) illustrate the degree of disease reduction obtained by applications of the various tested fungicides. Products that provided most effective control against the disease include Orondis ultra, Zampro, Stargus, Cevya, Eject .Please see table for other treatments with significant disease suppression/control. No phytotoxicity was observed in any of the treatments in this trial.
In previous articles, I have discussed using band-steam to control plant diseases and weeds. Band-steam is where, prior to planting, steam is injected in narrow bands (4” wide x 2” deep), centered on the seedline to raise soil temperatures to levels sufficient to kill weed seed and soilborne pathogens (>140 °F for >20 minutes). After the soil cools (<1 day), the crop is planted into the strips of disinfested soil.
This summer, project Co-PI, Steve Fennimore, Extension Specialist – Weed Science, UC Davis has been evaluating the efficacy of using band-steam to control weeds and cavity spot (Pythium spp.) in carrot. The trials are still in progress, but so far, the technique has been found to be very promising for weed control (Fig. 1).
Using steam to control weeds in high density crops such as carrot, baby leaf spinach and spring mix may be a particularly good fit for the method. Handing weeding in these crops is labor intensive and costs are high, typically exceeding $300/acre (Fig. 2). Costs are even greater in organic crops. A benefit of steam application is that it is organically compliant.
This fall, we will be developing a steam applicator designed for use on wide beds. We’ll be trialing the device in baby leaf spinach and spring mix. If you are interested in this application, we’ll be demonstrating weed control in baby leaf spinach using steam heat at the UA 3rd AgTech Field Day. The event will be held Tuesday, October 25th at the Yuma Ag Center.
Acknowledgements
This work is supported by the Arizona Specialty Crop Block Grant Program and the Crop Production and Pest Management grant no. 2021-70006-35761 /project accession no. 1027435 from USDA-NIFA. We appreciate their support. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
Fig. 1. Weed control with band steaming in carrot. Steam was applied in a 4-inch band centered on the two seedlines (between the dashed white lines) prior to planting. The weeds outside of the treated band can be easily removed through cultivation. (Photo credits: Steve Fennimore, UC Davis).
Fig. 2. Hand weeding in crops seeded at high densities is labor intensive.
One of our local PCAs (Pest Control Advisors) in Yuma, Arizona found Buffalobur nightshade last week in an artichoke field in the area.
Buffalobur is a summer annual that belongs to the Solanaceae family. Another weed from this family commonly seen is Silverleaf nightshade (Solanum eleagnifolium). Unlike Silverleaf that has a purple flower, Buffalobur has a yellow flower. Leaves are deeply lobed from half to all the way to the midrib resembling small watermelon leaves. Sometimes toothed, the leaves are alternate on the stems with star-shaped hairs and are TOXIC TO HUMANS AND LIVESTOCK.
Animals would have to consume 0.1-0.3 % of their bodyweight to have toxic effects. Goats and sheep are more resistant than cattle to the weed's glycoalkaloid solanine, which is the toxic agent [3].
Its named Buffalobur for the prickly burs that got entangled to the fur of the bisons. Plants can reach up to 60 cm tall [2].
This weed is a natural host of the Colorado Potato Beetle (Leptinotarsa decemlineata). It is also an alterative host of some mosaic virus affecting potato, tomatoes, and alfalfa. Additionally, it can harbor nematodes that are damaging to tomatoes [1].
According to the National Noxious Weed Control Board 2,4-D and Banvel are herbicides that provide complete control of this weed [3].
If infestations are small, it is also recommended to remove plants wearing sturdy gloves. The objective is to prevent the mature burs from releasing seeds when dehiscence occurs increasing the infestation.
Thank you for sharing your findings with the University of Arizona Vegetable IPM Team.
Image Courtesy of Jim Daily
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